In many battery powered devices, there is frequently a need to balance power consumption and latency, or the speed with which the device responds to user input. Wireless computer input devices such as a computer mouse are but one example. As is known, a computer mouse generally includes motion detection components, internal circuitry for converting the detected motion into data that can be transmitted to a computer, and one or more buttons, scroll wheels, etc. In the case of a wireless mouse, the mouse further contains circuitry for wireless (typically RF) communication with a receiver that is connected to a computer. All of these mouse components require power to function, and the mouse consumes more power if these components are used more frequently.
The problem has become more acute with the advent of optically tracking mice. Unlike earlier designs in which motion is detected by a series of encoder wheels that are rotated by a rolling ball, optical mice do not require moving parts to detect motion (other than the mouse itself relative to some surface). Instead, an optical mouse takes a series of images of the surface over which it moves, and then compares the images to determine the direction and magnitude of motion. Examples of such optical input devices are described in, e.g., U.S. Pat. No. 6,303,924 (titled “Image Sensing Operator Input Device”) and U.S. Pat. No. 6,172,354 (titled “Operator Input Device”). As described in those patents, an array of photo-sensitive elements generates an image of a desktop (or other surface) portion when light from an associated illumination source reflects from the desktop or other surface.
Optical input devices offer a number of advantages over devices that mechanically encode motion. However, optical devices often consume more power than mechanical designs. This is largely due to the light source that such a device uses to create an image of the desktop or other surface. Often, a Light Emitting Diode (LED) is energized and shined on the surface to be imaged. A semiconductor laser source (such as a VCSEL, or Vertical Cavity Surface Emitting Laser) may also be used. An optically tracking input device may have a substantially reduced battery life by comparison to a mechanically tracking device. Because of this, a compromise must generally be made between power consumption and performance. For example, an optical computer mouse tends to provide faster and more precise motion detection as the rate of imaging increases, i.e., by taking more image frames per second. However, more images per second require the mouse's light source to be energized more frequently, thus drawing more power. Similarly, more frequent imaging requires increased computational activity to translate the increased number of images into data for transmission to the computer. This further requires additional power, as does the transmission of the additional data.
Wireless computer mice and other peripherals are becoming increasingly popular with computer users. Such devices often eliminate clutter and inconvenience caused by cables, are often easier to connect to a computer, and may be more suitable for use with a computer in certain locations (e.g., the kitchen or living room of a home). So as to conserve power, many wireless mice and other input devices are configured to “sleep,” or to cease certain functions during periods of non-use. For example, some computer mice are configured to reduce imaging (and data reporting) frequency after a certain period of non-movement and lack of user input to a mouse button or scroll wheel. After a certain period of such non-activity, it is assumed the mouse is not needed, and the imaging frame rate decreased. Instead of generating frequent images to detect the amount and direction of movement, the mouse generates relatively infrequent images so as to only determine whether movement has occurred at all. If motion is detected, it is assumed that the mouse is again needed, and the frame rate increased. Although such methods can prolong battery life, they are a further source of latency which may be perceivable by a user. In particular, the reduced sleep mode frame rate, in combination with the time required to return to an “awake” mode, is perceptible to many users as a time lag between touching a sleeping mouse and the generation of a corresponding cursor movement or other screen activity. Although this problem can be alleviated somewhat by increasing the period of non-activity necessary to put the mouse “to sleep,” this also increases power consumption. Moreover, it is often difficult to find the best time period for every user and software application.
Balancing performance and power consumption thus presents a significant problem in the design of wireless battery operated input devices. The problem is exacerbated by the widely varying differences among the performance requirements and preferences among different computer users and computer applications. Computer gamers, for example, often desire extremely fast response times. Other persons may use a computer for word processing and other office applications, Worldwide Web (WWW or Web) browsing and other less performance-intensive activities. These persons may instead be more concerned with frequent battery replacement. Accommodating such diverging requirements has proved difficult. In some cases, designers have created complex power management algorithms based on actual data gathered from users. These algorithms have not always been completely successful, and there remains a need for improved methods and systems for balancing performance and power use.